I checked the sag on my 07 CRF 450. The sag is high (112mm). The static sag is 25mm. What effect will this have on the bike? Do I need a new spring? Will it get taller as I adjust the sage back to 100mm? I'm only 5'8" so I may need to look at a lowerd seat if it gets much taller.

It seems to ride fairly well in casual riding, but on a MX track its different. I'm new to mx so I'm sure a lot of the unsteadiness is just due to my lack of MX skills, but some info about which direction I should go would be helpful.

you need a stiffer spring

Supposedly the guy I bought it from had it respung for his 200 pound weight. I only weigh 180, so it should be too firm. The measurements dont back that up.

Could the nitrogen in the shock be low? How would I check?

I think you need to go back to square one and set your sag to 100ish then check free sag, take an average free sag by pushing down on the seat slightly and letting the bike extend back up on it's own then, write that measurement down, then lift up on the seat and let the bike settle on it's own, measure again and average the two for a better idea of your actual free sag. The only good way to know if nitro is at spec is to service the shock. The volume of the bladder is too small to check with a guage. You can pull the spring and push the rod to see if it extends, but that won't tell you how close to manual spec your psi is.

what your describing is too stiff a spring. I think if you had 100mm race sag and 25mm static you would need a stiffer one but that's not your case, it's the opposite.

Do yourself a favor and dont cut the seat. I'm 5'4" and I ride with stock height on everything. My race sag is at 111-112mm and the bikes handle great. I cant hardly touch ground on either of my YZ's. Cutting the seat messes up your geometry when turning. You cant get far enough up on the tank when needed. 5'8" man I wish I was that tall.:worthy:

chadk66 said:

No, his numbers are saying to soft a spring.

doc

too soft

I took the sub frame off today for a look. The shock was out of spec on the pre-load length. Standard length is 10.11 inches according to my manual. The length in the bike was 10.5".

If I turn the lock rings in (clockwise) to 10.11" that should increase the pre-load. If I am reading the manual right that would also stiffen the shock and decrease the static sag and the race sag at the same time. That should get me closer to where I need to be and I can recheck the race sag and adjust from there. Is this correct?

no matter what you do, it's a waste of time.
The spring is too soft, so turning it in, out, up, down, right, left, painting it black, green, yellow or whatever you do doesn't change anything on the fact that you need a stiffer spring to get your sag within the ballpark.

dogfish said:

did you seriously just try saying that cutting the seat messed with the geometry, but running the sag to low sn't messing with the geometry?

Get the right spring, forget what the 200 lb guy said, and if you are short then you can use more rear sag as long as you also lower the front (forks up in the clamps) to match. This works for me.

100mm is a sane starting point for most bikes, but it assumes correct springs, suitable fork height, and reasonable damper settings.

eg. forks up 10mm and springs are right both ends, then 105mm rear sag might be just fine.

Front and rear heights must match to get the right turning and stability behavior. It's super fundamental to bike setup. Get the right springs and dont adjust rear sag for any other purpose than changing turning or stability. Find a nice moderately berm turn, then try the rear too high and too low, and you should quickly feel what's going on.

You probably know that measuring rear sag is difficult on your own. You need wear at least your helmet and boots, and you need to be in the riding position. Well I think it's more important to be in a reproducible position so you can compare next time, so I just stand up straight on the pegs with one finger balancing me on a wall, while my assistance measures.

Ttoks said:

Yes I did. Think about it...lowering lets say 140lbs(me) down 1-2 inches and back has a larger affect on turning than running an extra 1-2mm of sag. My suspension tuner says there is nothing wrong with running 100-112mm of sag on the YZ. as long as the clicker settings result in the bike balanced front to back.

dogfish said:

That aint the case on my KX450F. 1mm of sag change has a much greater impact on how my bike turns in and tracks thru a corner than when I put my 1" lower SDG seat on.

Sag impacts the geometry big time. The weight bias and also the steering rake and trail. I've no idea why it's so sensitive, at least on some bikes - like mine. Get it right and riding is like night vs day easier.